1 :mod:`atexit` --- Exit handlers 2 =============================== 3 4 .. module:: atexit 5 :synopsis: Register and execute cleanup functions. 6 .. moduleauthor:: Skip Montanaro <skip (a] pobox.com> 7 .. sectionauthor:: Skip Montanaro <skip (a] pobox.com> 8 9 10 .. versionadded:: 2.0 11 12 **Source code:** :source:`Lib/atexit.py` 13 14 -------------- 15 16 The :mod:`atexit` module defines a single function to register cleanup 17 functions. Functions thus registered are automatically executed upon normal 18 interpreter termination. :mod:`atexit` runs these functions in the *reverse* 19 order in which they were registered; if you register ``A``, ``B``, and ``C``, 20 at interpreter termination time they will be run in the order ``C``, ``B``, 21 ``A``. 22 23 **Note:** The functions registered via this module are not called when the 24 program is killed by a signal not handled by Python, when a Python fatal 25 internal error is detected, or when :func:`os._exit` is called. 26 27 .. index:: single: exitfunc (in sys) 28 29 This is an alternate interface to the functionality provided by the 30 :func:`sys.exitfunc` variable. 31 32 Note: This module is unlikely to work correctly when used with other code that 33 sets ``sys.exitfunc``. In particular, other core Python modules are free to use 34 :mod:`atexit` without the programmer's knowledge. Authors who use 35 ``sys.exitfunc`` should convert their code to use :mod:`atexit` instead. The 36 simplest way to convert code that sets ``sys.exitfunc`` is to import 37 :mod:`atexit` and register the function that had been bound to ``sys.exitfunc``. 38 39 40 .. function:: register(func[, *args[, **kargs]]) 41 42 Register *func* as a function to be executed at termination. Any optional 43 arguments that are to be passed to *func* must be passed as arguments to 44 :func:`register`. It is possible to register the same function and arguments 45 more than once. 46 47 At normal program termination (for instance, if :func:`sys.exit` is called or 48 the main module's execution completes), all functions registered are called in 49 last in, first out order. The assumption is that lower level modules will 50 normally be imported before higher level modules and thus must be cleaned up 51 later. 52 53 If an exception is raised during execution of the exit handlers, a traceback is 54 printed (unless :exc:`SystemExit` is raised) and the exception information is 55 saved. After all exit handlers have had a chance to run the last exception to 56 be raised is re-raised. 57 58 .. versionchanged:: 2.6 59 This function now returns *func*, which makes it possible to use it as a 60 decorator. 61 62 63 .. seealso:: 64 65 Module :mod:`readline` 66 Useful example of :mod:`atexit` to read and write :mod:`readline` history files. 67 68 69 .. _atexit-example: 70 71 :mod:`atexit` Example 72 --------------------- 73 74 The following simple example demonstrates how a module can initialize a counter 75 from a file when it is imported and save the counter's updated value 76 automatically when the program terminates without relying on the application 77 making an explicit call into this module at termination. :: 78 79 try: 80 _count = int(open("counter").read()) 81 except IOError: 82 _count = 0 83 84 def incrcounter(n): 85 global _count 86 _count = _count + n 87 88 def savecounter(): 89 open("counter", "w").write("%d" % _count) 90 91 import atexit 92 atexit.register(savecounter) 93 94 Positional and keyword arguments may also be passed to :func:`register` to be 95 passed along to the registered function when it is called:: 96 97 def goodbye(name, adjective): 98 print 'Goodbye, %s, it was %s to meet you.' % (name, adjective) 99 100 import atexit 101 atexit.register(goodbye, 'Donny', 'nice') 102 103 # or: 104 atexit.register(goodbye, adjective='nice', name='Donny') 105 106 Usage as a :term:`decorator`:: 107 108 import atexit 109 110 @atexit.register 111 def goodbye(): 112 print "You are now leaving the Python sector." 113 114 This only works with functions that can be called without arguments. 115
